金属元素替代对Li4BN3H10储氢材料释氢影响机理的第一性原理研究

应用基于密度泛函理论的赝势平面波第一性原理方法研究了金属元素替代对Li₄BN₃H₁₀ 释氢的影响机理.计算给出了结合能、电子态密度、密集数, 分析了结构的稳定性和原子间的成键情况.结果表明: 晶体的结合能与(LiM)₄BN₃H₁₀(M=Ni,Ti,Al,Mg)释氢性能没有直接的关联.带隙的宽窄和带隙中是否存在杂质能级是决定(LiM)< 关键词： LiBNH系储氢材料 第一性原理 元素替代 释氢机理     

Properties of nuclear matter andN=Z closed-shell nuclei

A simple three-parameter density dependent effective interaction is used to study the properties of nuclear matter, neutron matter and some bulk properties such as ground state energies and rms charge radii of three double-closed shell nuclei⁴He,¹⁶O and⁴⁰Ca. The three parameters of the effective interaction are determined by requiring to fit the binding energy and density of infinite nuclear matter at saturation density as well as ground state energy of¹⁶O in the first order perturbation theory. This interaction gives correct saturation in nuclear matter with a value of 283 MeV for compressibility. The symmetry coefficienta _T atk _F=1·36 fm^–1 is 28·58 MeV. The energy per particle in neutron matter is calculated in the range of nuclear matter densities and it compares well with those ofNemeth andSprung. Groundstate energies and rms charge radii of⁴He,¹⁶O and⁴⁰Ca are calculated using oscillator eigen functions as single particle wave functions. Results for ground state energies are in good agreement with empirical values and rms charge radii are slightly better than those obtained byMoszkowski with the MDI.The authors are thankful to the Computer Centre, Utkal University, Bhubaneswar for providing computational facilities for this work.     

Caged H atom and H2 molecule in relation to Monte Carlo study of molecular dissociation at constant volume

Summary Analytic results for electronic kinetic energy are first presented for a hydrogen atom in a spherical cage for two radii near to the corresponding densities employed in the path-integral Monte Carlo study of isochoric molecular dissociation in dense hydrogen by Magroet al. (Magro W. R., Ceperley D. M., Pierleoni C. andBernu B.,Phys. Rev. Lett.,76 (1996) 1240). The relevance of the ?cage? results to the behaviour of dense atomic hydrogen is pointed out. Attention is then shifted to the molecular regime, and the variation with density of electronic kinetic energy for a H₂ molecule in a rigid spheroidal cage is compared and contrasted with the Monte Carlo findings. The rigid-cage model mimics this, as well as bond length contraction, under compression.     

Swift heavy ion irradiation effects on structural,optical properties and ac conductivity of polypyrrole nanofibers

Polypyrrole (PPy) nanofibers have been synthesized by interfacial polymerization method and irradiated with 160?MeV Ni¹²⁺ ions under vacuum with fluences in the range of 10¹⁰–10¹²?ions/cm². High-resolution transmission electron microscopy results show that upon swift heavy ion (SHI) irradiation the PPy nanofibers become denser. The crystallinity of PPy nanofibers increases upon SHI irradiation, while their d-spacing decreases. Upon SHI irradiation, the polaron absorption band gets red-shifted indicating reduction in the optical band gap energy of the irradiated PPy nanofibers. The indirect optical band gap energy is decreased as compared to corresponding direct optical band gap energy. The number of carbon atoms per conjugation length (N) and carbon atoms per cluster (M) of the SHI-irradiated PPy nanofibers increase with increasing the irradiation fluence. Fourier transform infrared spectra reveal the enhancement in intensity of some characteristic vibration bands upon SHI irradiation. The thermal stability of the PPy nanofibers is enhanced on SHI irradiation. The charge carriers in both pristine and irradiated PPy nanofibers follow the correlated barrier hopping mechanism. Scaling of ac conductivity reveals that the conduction mechanism is independent of the SHI irradiation fluence.     

Structural, electronic and vibrational properties of indium oxide clusters

Geometric, electronic and vibrational properties of the most stable and energetically favourable configurations of indium oxide clusters In_mO_n (1≤m, n≤4) are investigated using density functional theory. The lowest energy geometries prefer the planar arrangement of the constituent atoms with a trend to maximize the number of ionic In-O bonds. Due to the charge transfer from In to O atoms, the electrostatic repulsion occurs between the atoms with the same kind of charge. The minimization of electrostatic repulsion and the maximization of In-O bond number compete between each other and determine the location of the isometric total energy. The most stable linear In-O-In-O structure of In₂O₂ cluster is attributed to the reduced electrostatic repulsive energy at the expense of In-O bond number, while the lowest energy rhombus-like structure of In₂O₃ cluster reflects the maximized number of In-O bonds. Furthermore, the vibrational frequencies of the lowest energy clusters are calculated and compared with the available experimental results. The energy gap and the charge density distribution for clusters with varying oxygen/indium ratio are also discussed.     

Ground state of aD − ion in semiconductors

The mechanisms that feature in the formation ofD ^– ions in spherical band semiconductors are discussed. Analogies are drawn with H^– formation (a proton binding two electrons). The variational method is applied in calculating the binding energy of the extra electron in the absence of external magnetic field. The binding energies obtained with different trial functions are compared with that extrapolated from experimental measurements. From such a comparison it is clear that a simple trial function with only one variational parameter involving the screening of the positive charge of the nucleus gives good results.     

Decay reactions of rare gas cluster ions: Kinetic energy release distributions and binding energies

We have carried out measurements on metastable fragmentation of mass selected argon cluster ions which are produced by electron impact ionization of a neutral argon cluster beam. From the shape of the fragment ion peaks (MIKE scan technique) one can deduce information about the distribution of kinetic energy that is released in the decay reaction. In this study, for Ar ₅ ⁺ to Ar ₁₅ ⁺, it is Gaussian and thus we can calculate from the peak width the mean kinetic energy release 〈KER〉 of the corresponding decay reactions. Using finite heat bath theory we calculate from these data the binding energies of the decaying cluster ions. Received 20 November 2000     

Theoretical analysis of spin-Hamiltonian parameters for the rhombic Cu2+ centres in CuGaSe2 crystals

The spin-Hamiltonian parameters (g factors g_i and hyperfine structure constants A_i, where i = x, y, z) of the rhombic Cu²⁺ centres in the CuGaSe₂ crystal are determined from the high-order perturbation formulae based on the cluster approach (sometimes also called two-spin-orbit parameter model). In the studies, some parameters in the analysis of g factors for the same centre within the tetragonal symmetry approximation in the previous paper are used, and the parameter due to the perturbation of rhombic crystal field caused by a charge compensator at, e.g., [110] direction are considered. As the result of a fitting process, the determined spin-Hamiltonian parameters are in reasonable agreement with the experimental values. The results are discussed.     

WnNim(n+m=8)团簇结构与电子性质的理论研究

采用密度泛函理论(DFT)中的B3LYP方法,在Lanl2dz基组水平上对W_nNi_m(n+m=8)团簇的各种可能构型进行了几何参数全优化,得到了它们的基态构型;并对基态构型的平均结合能、Wiberg键级(WBI)、磁学性质、NBO进行了分析,结果表明:团簇随着W原子数的增多,稳定性增强,n≥5时,结构中都含有纯钨团簇的结构基元;W-W键级高于W-Ni键和Ni-Ni键;W₅Ni₃,W₆Ni₂团簇发生了"磁矩猝灭"的现象;在W,Ni原子内部,轨道电荷发生了转移,产生了"轨道杂化"现象,W,Ni原子之间也发生了电荷转移形成了较强的化学键. 关键词： nNi_m(n+m=8)团簇')" href="#">W_nNi_m(n+m=8)团簇 几何结构 电子性质 密度泛函理论     

密度泛函理论研究Hg与Auqn(n=1—6, q=0,+1,-1) 团簇的相互作用

采用密度泛函理论中的广义梯度近似对Hg与小团簇Au ^q_n (n=1—6, q=0, +1, -1)的相互作用进行了系统研究. 结果表明,除Au₅^+,-团簇外,前线分子轨道理论可以成功预测大部分Au _n Hg ^q 复合物的最低能量结构. Au_n团簇对Hg的吸附受团簇尺寸大小和团簇所携带电荷的影 关键词： 密度泛函理论 汞 金团簇 吸附能     

A refined potential energy surface and the rovibrational states for the electronic ground state of ozone

A potential energy surface for the electronic ground state of ozone has been optimized by using a variational procedure with the exact vibrational Hamiltonian in bond length-bond angle coordinates. In the optimization, the ab initio force field of Borowski, P., Andersson, K., Malmquist, P.-A., and Roos, B. O., 1992, J. chem. Phys., 97, 5568 is taken as the starting point, and the recent observed vibrational band origins up to 4900 cm^-1 reported by Floud, J.-M., Barbe, A., Camy-Peyret, C., and Plateaux, J. J., 1996, J. molec. Spectrosc., 177, 34 are involved. The root mean square error of this fit for the 39 observed vibrational energy levels is 0.83 cm^-1. In order to test the refined potential, the rovibrational energy levels up to J = 15 are calculated and compared with the observed values.     

Electronic and optical properties of pure and Ce3+-doped CaS single crystals: a first-principles prediction

This paper investigates the electronic and optical properties for pure and Ce 3+-doped CaS crystals by using the first-principles total energy calculations.The results show that CaS:Ce has a direct band gap of 2.16 eV,and the top of the valence band is determined by S 3p states and the bottom of the conduction band is determined by Ce 4f states,respectively.Our results validate that the yellow emission from CaS:Ce is produced by doped cerium and the green emission quenches at 12.5% cerium concentration.The Ce-S bond shows more covalent character than the Ca-S bond.     

Weak gamma-ray transitions of 1·440 MeV and 1·460 MeV in the decay of207Bi

The single gamma-ray spectra of²⁰⁷Bi were measured with 32 c. c. Ge(Li) detector. Evidence of gamma transitions of energies 1·440 MeV and 1·460 MeV is found. The relative intensity of these lines has also been estimated by measuring their photopeak areas. There is no evidence of the weak 0·9 MeV gamma as reported earlier (Alburger D. E.,Sunyar A. W., Phys. Rev.99 (1955), 695;Jar Dine L. J., Phys. Rev.C 11 (1975), 1385).The authors are grateful to the Director of the Saha Institute of Nuclear Physics, Calcutta for providing the facilities to work with the Ge(Li) detector at the Institute. We wish to thank Professor B. B.Baliga of the Institute for valuable discussions. Our thanks are due to Professor B. P.Singh, Head of the Physics Department of Roorkee University, Roorkee, for providing us with the facilities to perform the coincidence measurements in his laboratory.     

Rate constant of capture of electron charge carriers on a screened repulsive center

The rate constant of capture of electron charge carriers on a screened repulsive center are performed. Approximate expressions for the potential barrier width, the capture cross section, and rate constant are derived. It is shown that the increase in the concentration of free charge carriers in silver azide from 10¹⁶ to 10²⁰ cm^?3 results in an increase in the capture rate constant by four orders of magnitude. It is also shown that, with increasing concentration of free carriers, the temperature dependence of the rate constant weakens and the effective activation energy of capture in silver azide decreases from 0.18 to 0.01 eV.     

Ab-initio Study of Small Silver Nanoclusters

We explore the lowest energy structures and investigate the structural and electronic properties of small Ag_N (N = 1–10) clusters by employing an ab-initio self-consistent density functional method in the local density approximation. The calculation of binding energy, bond length and the energy difference of HOMO–LUMO states have been carried out in a large energy interval for different isomeric forms of Ag clusters. The cluster binding energies increases rapidly with cluster size, which is consistent with the size dependence properties of clusters but our values are slightly higher than the other calculations.     

Two-photon excitation spectrum of benzonitrile vapour

The two-photon excitation spectrum of benzonitrile in the gas phase at about 1 torr has been recorded and analysed in the total energy region of 36300 to 40500 cm⁻¹ using both linearly and circularly polarised light from a Nd-YAG pumped dye laser. The two-photon spectrum consists of strong Franck Condon (fc) transitions bearing a good resemblance to the one-photon spectrum and also vibronic coupling (vc) transitions essentially arising out of the analogue of the benzeneν ₁₄. By a comparative study of thetp spectra of various other monosubstituted benzenes, it has been inferred that the strongtp spectrum of benzonitrile should be ascribed to a considerableπ charge delocalization over the phenyl and nitrile groups.     

(HMgN3)n(n=1–5)团簇结构与性质的密度泛函理论研究

利用密度泛函理论在B3LYP/6-311G^*水平上对叠氮化合物(HMgN₃)_n(n=1–5)团簇各种可能构型进行了几何优化,预测了各团簇的最稳定结构. 并对最稳定结构的成键特性、电荷分布、振动特性及稳定性进行理论研究. 结果表明:HMgN₃团簇最稳定结构为直线型;(HMgN₃)_n(n=2,5)团簇最稳定结构为叠氮基中N原子和金属原子相连构成Mg–N–Mg结构;(HMgN₃)_n(n=3,4)团簇最稳定结构为叠氮基与Mg原子相互链接形成的环状结构. 团簇最稳定结构中金属Mg原子均显示正电性,H原子均显示负电性,叠氮基中间的N原子显示正电性、两端的N原子显示负电性,且与Mg原子直接作用的N原子负电性更强. Mg–N键和Mg–H键为典型的离子键,叠氮基内N原子之间是共价键. 团簇最稳定结构的红外光谱分为三部分,其最强振动峰均位于2258–2347 cm^-1,振动模式为叠氮基中N–N键的反对称伸缩振动. 叠氮基在团簇和晶体中结构不变,始终以直线型存在. 稳定性分析显示,(HMgN₃)₃团簇相对于其他团簇更为稳定. 关键词： 3)_n(n=1–5)团簇')" href="#">(HMgN₃)_n(n=1–5)团簇 叠氮基 密度泛函理论 结构与性质     

The existence of (n, γf) process on235U nucleus and uranium X-ray yields

The measurement of X-rays emitted before the fission of²³⁵U induced by resonance neutrons is described. Preliminary results show the dependence of the X-ray yield on fission width _f. It is explained on the bases of the existence of the two-step (n,f) process. The estimate of the width of the (n,f) process is of the order of 4 MeV and the-transitions taking place before fission of²³⁶U compound nucleus are mostly of the M1 type.In conclusion the authors would like to express their gratitude to L. B.Pikelner for many useful discussions, to I. M.Salamattn and A.Mateeva for the programme supply of the experiment, V. G.Tisin, A. A.Bogdzel, Yu. I.Kolgin and N.Chikov for taking part in the different steps of the work. The authors are also grateful toYu. P.Popov and I.Wilhelm for taking interest in the work.     

Universal correlations in pion-less EFT with the resonating group method: Three and four nucleons

The Effective Field Theory “without pions” at next-to-leading order is used to analyze universal bound-state and scattering properties of the 3- and 4-nucleon system. Results of a variety of phase shift equivalent nuclear potentials are presented for bound-state properties of ³H and ⁴He , and for the singlet S -wave ³He -neutron scattering length a ₀(³He-n) . The calculations are performed with the Refined Resonating Group Method and include a full treatment of the Coulomb interaction and the leading-order 3-nucleon interaction. The results compare favorably with data and values from AV18(+UIX) model calculations. A new correlation between a ₀(³He-n) and the ³H binding energy is found. Furthermore, we confirm at next-to-leading order the correlations, already found at leading order, between the ³H binding energy and the ³H charge radius, and the Tjon line. With the ³H binding energy as input, we get predictions of the effective field theory “without pions” at next-to-leading order for the root mean square charge radius of ³H of (1.6±0.2) fm, for the ⁴He binding energy of (28±2.5) MeV, and for Re{a ₀(³He-n)} of (7.5±0.6) fm. Including the Coulomb interaction, the splitting in binding energy between ³H and ³He is found to be (0.66±0.03) MeV. The discrepancy to data of (0.10±0.03) MeV is model independently attributed to higher-order charge independence breaking interactions. We also demonstrate that different results for the same observable stem from higher-order effects, and carefully assess that numerical uncertainties are negligible. Our results demonstrate the convergence and usefulness of the pion-less theory at next-to-leading order in the ⁴He channel. We conclude that no 4-nucleon interaction is needed to renormalize the theory at next-to-leading order in the 4-nucleon sector.     

Semiempirical molecular orbital calculations for four-, six- and eight-atom systems

The geometry, bond order, binding energy, ionisation potential, dipole moment and net charges have been calculated for cis-N₂O₂, trans-N₂O₂, N₂O₄, BF₃, CH₃, NH₃, BH₃ and B₂H₆ systems using semiempirical molecular orbital methodsindo and the results compared with available experimental,ab initio andmindo/3 data.